Process for converting high molecular weight paraffins to lower molecular weight paraffins of high octane value



United States Patent 3,242,222 PROCESS FOR CONVERTING HIGH MOLECULAR WEIGHT PARAFFINS TO LOWER MOLECULAR WEIGHT PARAFFINS OF HIGH OCTANE VALUE Patrick W. Ryan, Chicago Heights, lll., assignor to Sinclair Research, Inc., Wilmington, Del., a corporation of Delaware No Drawing. Filed Dec. 5, 1961, Ser. No. 157,268 8 Claims. (Cl. 260-676) This invention relates to the conversion of low octane number paraflinic feedstocks into high octane motor fuel components. More particularly the present invention is concerned with a conversion process wherein higher molecular weight parafiins are converted to lower molecular weight paraffins of high octane value.

The increasing use of high compression, spark ignition, internal combustion engines has brought about a growing demand for high octane number motor fuels. Accompanying this demand has been an increased desire for processing methods by which low octane parafiinic feedstocks, commonly available to refiner as by products of various petroleum refining operations, can be upgraded into high octane motor fuel components.

It has now been found that low octane, normally liquid isoparaffinic feedstocks, for instance, having a neat octane rating (RON), up to about 60, can be cracked utilizing a boron-trifluoride-phosphoric acid catalyst system into lower molecular weight paraffius of high octane value highly desirable as motor fuel components. Surprisingly high selective yields are obtained by the process of the present invention. Although the feedstock can be composed of pure isoparafiins alone, the present process is particularly advantageous where the feedstock is an admixture of isoparafiins and normal parafiins. The process of the present invention selectively converts the isoparafiins with little or no conversion of the normal parafiins. It does not require the addition of lower boiling isoparafiins such as isobutane and in fact makes at least 10% by weight, preferably 20% by weight of isobutane which can be utilized in other operations such as alkylation. Thus, because of this selective conversion, the present invention provides in addition a method for separating normal paraffins from a mixture of normal and isoparafiins of the same molecular weight range, the isoparaifins being readily removed by distillation as lower molecular Weight hydrocarbons.

In accordance with the present invention an isoparaffinic feedstock essentially of about 6 to 12, preferably 8 to 10, carbon atoms is contacted with a boron trifluoridephosphoric acid catalyst at a temperature of about 30 to 350 F., preferably about 150 to 250 F., and a BF partial pressure of about 100 to 5000 p.s.i.g., preferably about 600-1200 p.s.i.g. The hydrocarbons are contacted at least partially in the liquid phase with the catalyst for a time suflicient to produce lower molecular weight prodnets of high octane value, for instance isobutane, isopentane, etc. Normally, the contact period will be dependent on the stirring efficiency, temperature and BF}; partial pressure but will generally fall within the range of about minutes to 5 or more hours, preferably about 15 minutes to 1 hour. Advantageously, these reaction conditions are usually selected to provide conversion of at least about 50%, preferably at least about 70 or even at least about 90%, of the isoparaffin component of the feed to lower boiling hydrocarbons.

The phosphoric acid catalyst of the present invention is employed in effective catalytic amounts and will usually be present in the cracking zone in a weight ratio of about 0.1:1 to 10:1 of total hydrocarbon to catalyst, preferably in a weight ratio of about 1:1 to 2:1. The process may be carried out in a batch operation or in a continuous operation which provides for recycle of the catalyst. The hydrocarbon product and the phosphoric acid-boron trifluoride catalyst layers resulting on completion of the reaction can be separated by any manner desired. When agitation of the reaction mixture is stopped, it will separate into two phases in the reactor or in any other vessel into which it is transferred as in a continuous or batch operation. These phases can be separated by simple decantation.

The reaction mixture can be allowed to separate into a lower layer of catalyst containing unsaturated oil including aromatics. The upper hydrocarbon layer formed can be freed from the catalyst by distillation and/or washing with water or passed through a column of basic ion exchange resin or other solid absorbent such as charcoal, potassium sulfate, sodium sulfate, etc. The unsaturated oil (catalyst oil) appearing in the catalyst layer can be separated through discharge into water followed by extraction with a solvent, e.g., ether or pentane. Small traces of fluoride remaining in the hydrocarbon material can be removed as by contact with alumina at about 200 to 500 F. Various drying procedures can be employed to separate the water from the hydrocarbon materials. Preferably the reaction product is characterized, aside from the C s by predominantly a C to C fraction with C being a major component.

As aforementioned, the reaction of the present invention is conducted under a B1 partial pressure of about 100 to 5000 p.s.i.g. In operation, therefore, phosphoric acid is saturated with BF and an excess BF pressure maintained. It is preferred that the phosphoric acid saturated with BF be about 40 or 50% to 100% concentration in water. The more concentrated phosphoric acid is preferred, e.g., at least about since with increasing concentration there is less consumption of boron trifiuoride. With phosphoric acid, for instance, one mole of boron trifluoride is absorbed per mole of acid while in the case of aqueous solutions both the phosphoric acid and water absorb boron trifluoride approximately mole for mole. The phosphoric acid-boron trifluoride catalyst system may be preformed, that is, formed prior to addition of the hydrocarbon or formed in situ, that is, after addition of the hydrocarbon and phosphoric acid to the reaction zone.

The hydrocarbon feed of the present invention contains an isoparaffin feed of about 6 to 12 carbon atoms. It can be pure isoparaflin alone or mixed. with n-paraffins but is more advantageously a paraffinic petroleum fraction in the C to C boiling range that contains at least some isoparaffins. The minimum amount of isoparaffins in the fraction is a matter of economics but usually the fraction contains at least about 30% by weight isoparafiins, more preferably, at least about 50 or even 70%. by weight isoparafiins, in admixture with normal parafiins and perhaps other hydrocarbons of similar boiling range. Such materials are found in various petroleum refinery streams and can be separated in more or less pure form. Large amounts of olefins may be excluded from the reaction system and anessentially olefin-free feedstock, for instance, having not more than about 5% olefins is preferred.

A particularly suitable feedstock is a parafiinic concentrate derived from the C liquid product contained in the elfiuent of reforming systems employing petroleum gasoline feedstocks and platinum-alumina catalysts. As

an example, most if not all of the aromatics of the separated by solvent extraction through the use of a solvent selective for aromatics, e.g., phenol, or by any other desirable procedure.

A particularly useful method for accomplishing this separation employs a glycol-water extraction medium. As commercially licensed, one such system is known as Udexing. By regulation of conditions such as a glycol to water ratio, the extraction and solvent stripping temperature, and the character of the glycol, a Udex rafiinate varying in paraffinicity is obtained. The manner of controlling these factors is known in the art and it is sufficient to say that the preferred glycol materials are the glycols such as diethylene and dipropylene glycols and their mixtures.

The following example will serve to further illustrate the present invention.

Example Three separate feeds, a dimethylhexane mixture, Udex raffinate, and n-octane were cracked as follows. A boron trifluoride saturated solution of 80% phosphoric acid was charged to a one gallon autoclave. The temperature was raised to approximately that indicated in Table I below and the feed was pressured into the reactor by means of a calibrated blow case. The Udex raffinate employed analyzed as follows:

Octane number (RON-k3 cc. TEL added/ gal.) 60.8

The reactor was then pressured up with the BF- to that indicated in Table I below and stirred for 2 hours after which stirring was stopped. The reactor was then cooled. The contents of the reactor were drained into a room temperature trap, which was in reality a separatory funnel. The room temperature trap was connected to a series of 4 cold traps where condensable gases were collected. After the catalyst was collected in the room temperature trap it was drained and stored in a stoppered bottle. The hydrocarbon in the room temperature trap was collected and weighed. The hydrocarbon present in each of the 4 cold traps was also weighed. The hydrocarbon products (excluding catalyst oil) were combined and analyzed. The results of each run and the conditions employed are shown in Table I.

TAB LE I.-C RACKIN G Run Number 7O 73 68 Feed Dimethyl- Udex n-Octane hexane Raliinate Catalyst 85% 85% 85% :H3PO4/BF3 H3PO4/BF3 H3PO4/BF3 Catalyst/HC Wt. Ratio 2 1 2 Temperature, F 250 250 248 Pressure, p.s.i.g. 985 800 980 Wt. Percent Recovery 95. 3 92. 4 94. 6 Wt. Percent Cat. OiL..- 19.1 16.4 4.7 Product Distribution, Wt.

Percent:

1.4 Trace 26. 4 l. 3 l. 7 0. 3 17. 8 1. 7 1.0 0.2 0. 1.0 3. 8 0.5 3. 2 0. 2 18. 0 90.1 1.2 0.1 Catalyst Oil 19.1 16. 4 ISO/normal butane ratio (theoretieal) 8.1 (2. 15. 5 (2. 5) Iso/normal pentane ratio (theoretical). 10. 2 (6. l) 17. 8 (6.1)

The data in Table I illustrate the selective nature of the catalyst system of the present invention toward isoparaffinic hydrocarbons. A conversion of 97.5 weight percent was obtained with dimethylhexane as feedstock, whereas less than 10 weight percent n-octane was converted under the same conditions. In the case of the Udex rafiinate, a highly parafiinic feedstock in the C and C range, there is almost complete conversion of the isoparaifin components while the n-octane remains apparently untouched. Thus, normal paraffins can easily be separated from a mixed feedstock of isoparaffins boiling in the same molecular weight range. The data also show that the present invention is capable of converting low octane paraffin feedstocks containing isoparaffins into potential high octane motor fuel componentsas shown in the data by the high iso/ normal parafiin ratios obtained in the cracked product.

It is claimed: I p

1. In a method of converting low octane parafiinic feedstocks, the steps comprising contacting an isoparaffinic hydrocarbon feedstock consisting of 6 to 12 carbon atoms having not more than 5% olefins at least partially in the liquid state with a catalytic amount of phosphoric acidboron trifiuoride catalyst at a temperature of about 150 to 350 F. and having a boron trifluoride partial pressureof about 100 to 5,000 p.s.i.g. to obtain lower molecular weight hydrocarbons of increased octane value.

2. The method of claim 1 wherein the parafiinic feed stock is a mixture of isoparafiins and normally parafiins, said normal paraflins undergoing little conversion.

3. The method of claim 2 wherein the parafiinic feedstock contains at least about by weight of isoparaffins.

4. In a method of converting low octane parafiinic feedstock, the steps comprising contacting an isoparaflinic hydrocarbon feedstock consisting of 6 to 12 carbon atoms having not more than 5% olefins at least partially in the liquid state with a catalytic amount of phosphoric acid boron trifluoride catalyst at a temperature of about 200 to 275 F. and having a boron trifluoride partial pressure of about 600 to 1200 p.s.i.g., the weight ratio of total hydrocarbon to phosphoric acid catalyst being about 1 to 2: 1, to obtain lower molecular weight hydrocarbons of increased octane value. p

5. The method of claim 3 wherein the lower molecular weight hydrocarbons of increased octane value are separated from the normal paraffins by distillation.

6. The method of claim 4 wherein the paraffinic feedstock is a mixture of isoparafiins and normal parafiins, said normal paraffins undergoing little conversion.

7. The method of claim 6 wherein the paraffinic feedstock contains at least about 70% by weight of isoparaffins.

8. The method of claim 7 wherein the lower molecular weight hydrocarbons increased octane value are separated from the normal parafiins by distillation.

References Cited by the Examiner UNITED STATES PATENTS 11/1944 Beyerstedt 260683.44 6/1964 Ryan et al 260-683.44

OTHER REFERENCES ALPHONSO D. SULLIVAN, Primary Examiner. 

1. IN A METHOD OF CONVERTING LOW OCTANE PARAFFINIC FEEDSTOCKS, THE STEPS COMPRISING CONTACTING AN ISOPARAFFINIC HYDROCARBON FEEDSTOCK CONSISTING OF 6 T 12 CARBON ATOMS HAVING NOT MORE THAN 5% OLEFINS AT LEAST PARTIALLY IN THE LIQUID STATE WITH A CATALYTIC AMOUNT OF PHOSPHORIC ACIDBORON TRIFLUORIDE CATALYST AT A TEMPERATURE OF ABOUT 150 TO 350*F. AND HAVING A BORON TRIFLUORIDE PARTIAL PRESSURE OF ABOUT 100 TO 5,000 P.S.I.G. TO OBTAIN LOWER MOLECULAR WEIGHT HYDROCARBONS OF INCREASED OCTANE VALUE. 